In drilling a well, a drill string is used. The drill string can comprise a drill bit attached to sections of drill pipe. As the well is drilled, additional sections of drill pipe are added to the drill string until the well is drilled deep enough to reach a formation where substances, such as water, oil or gas, can be produced from the well. Some wells require both a vertical section and a horizontal section. Sections of pipe are joined together using threaded connections on the pipe. The drill string is rotated to turn the drill bit in order to drill the well. When the drill string is removed from the wellbore, the sections of pipe can be removed from the drill string one or more sections at a time.
To drill or service wells, known designs use a drawworks with a transmission to operate the block mechanism to raise and lower the drill string into the hole. When raising a drill string, the drawworks is driven from an electric, hydraulic or mechanical means to wind a cable around a drum pulling the blocks and string towards the crown. When lowering a drill string, the combined weight of the string and block assembly causes the string to be lowered into the hole. This process of lowering the string into the hole can cause the string to become stuck on long horizontal well applications. This is time consuming, and can substantially increase the time required to service a horizontal well, thus requiring additional equipment the complete the service operation of that well.
It is, therefore, desirable to provide an automated service rig that overcomes the shortcomings of the prior art and decrease the time required to drill and/or service wells.